94 EXPERIMENTS ON THE FROUDE. 
expected from carrying the propeller well away from the hull. This matter 
will be discussed more in detail in considering the thrust deduction and 
wake-gain. 
WAKE-GAIN AND THRUST DEDUCTION. 
The results of the investigations of 1910 can be conveniently presented 
to the mind by computing the wake, the thrust-deduction and the hull- 
efficiency in the conventional way as shown by the table on page 95: 
In that table the speeds, powers, revolutions and thrusts are taken 
directly from the mean curves of Figs. 6 to 10, Plates 40 to 44. 
The apparent slip is computed as usual by an equation having the form 
PFS IOUS 6 
fee (6) 
in which p is the pitch of the propeller in feet, 7 is the number of revolutions 
per minute and 101.3 is the factor for converting knots per hour into feet 
per minute. 
To determine the real slip the value of 
(1-s)?A 
5 
is computed by aid of equation (5) and the corresponding real slip is deter- 
mined by aid of the curve of Fig. 5, Plate 39. 
Having the real and apparent slips the wake is computed by the 
customary equation 
I—S 
1 On 
w=I- (7) 
in which s and s,, are the real and apparent slips. 
The resistance in pounds as given in Table I is taken directly from a 
curve in Fig. 25, Plate 56, which will be described with the work of 1911. 
It is enough to say now that this curve was obtained by towing the Froude 
with the propeller removed, and that the only change from the condition 
in 1910 was the addition of a fair-water 5 inches long that fined down the 
dead-wood to a width of half an inch; it is probable that this fair-water 
occupied the place of the eddy astern of the rudder-post. There is a chance 
that the resistance (1910) was actually greater than here recorded on account 
of the eddy, but comparison of the curve from towing the Froude with 
results of towing the 23.5 foot model in Washington indicates that the 
uncertainty is probably not large. 
